Fouling in industrial water systems occurs even in industrial water systems treated with the best water treatment programs currently available. When fouling occurs, the water system is negatively impacted by contamination including deposition of air-borne, water-borne and water-formed contaminants, process leaks, and other factors. If fouling is allowed to progress, the system can suffer from decreased operational efficiency, premature equipment failure, and increased health-related risks associated with microbial fouling.
Fouling can also occur due to microbial contamination. Sources of microbial contamination in industrial water systems are numerous and may include, but are not limited to, air-borne contamination, water make-up, process leaks, and improperly cleaned equipment. These microorganisms can establish microbial communities on any wetable or semi-wetable surface of the water system. More than 99% of the microbes present in the water process may be present on system surfaces.
The use of oxidizing biocides in biofouling control methods is well established. Common oxidizing biocides such as chlorine and bromine are effective biofouling control agents so long as they are maintained at effective concentrations in the water. Unless the concentrations of the biocides are effectively monitored, improper levels result in undesired microbial growth, scaling, corrosion, environmental impact, and increased cost that limit industrial applicability.
Developments in industrial water treatment incorporating higher pH values and corrosion inhibitors have driven interest in biocide systems other than chlorine. Bromine use in biofouling control usually occurs through addition of sodium bromide to the water system with an oxidizing agent such as chlorine gas or sodium hypochlorite. The result of this approach is the generation of hypobromous acid, which may require less biocide feed to maintain overall cleanliness than a comparable system operating on chlorine alone. However, many of the same compounds and conditions that reduce chlorine effectiveness also reduce bromine effectiveness.
U.S. Pat. No. 6,110,387 (hereinafter the '387 patent) entitled “SULFAMATE STABILIZATION OF A BROMINE BIOCIDE IN WATER” to Albemarle Corporation attempted to demonstrate the importance of manipulating the order of addition of active components to the water to be treated. Essentially, the '387 patent discloses effective biocidal activity is achieved by introducing sulfamate and water-soluble bromide to the system before the chlorine oxidant is added. Uncertainty of improved biocidal performance, cost-effectiveness, actual stabilization, and effects on the environment limit its application in biocidal control.
U.S. Pat. No. 6,478,972 entitled “Method of Controlling Microbial Fouling” to Acculab Co. discloses the use of hypobromous acid, HOBr, formed by the reaction between an aqueous solution of alkali or alkaline earth metal hypochlorite and a bromide ion source. The applicants describe aqueous hypochlorite solution, water-soluble bromide ion source, with sulfamate ion source as stabilizer as an improved anti-fouling system.
Despite ongoing research, an efficient strategy for feeding effective doses of bromide and stabilizer to water systems being treated with chlorine has not previously been described. Thus, the multiple problems in devising an efficient biofouling control system remain.